Self-adjusting rod mechanism for railway brake system



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SE ADJUS G ROD MECHA M RAIL-W BRAKE SYSTE Filed May 12. 1954 9 Sheets-Sheet 2 VENTOR.

ATTORNEYS THOM JAMES, JR.

June 10, 1958 v T. JAMES, JR 2,838,141

SELF-ADJUSTING ROD MECHANISM FOR RAILWAY BRAKE SYSTEM 9 Sheets-Sheet 3 Filed May 12. 1954 as 27 \60 26 I? INVENFOR.

THOMAS JAMES,JR.

ATTOR NEYS June 10, 1958 T. JAMES, JR 2,838,141

SELF-ADJUSTING ROD MECHANISM FOR RAILWAY BRAKE SYSTEM 9 Sheets-Sheet 4 Filed May 12. 1954 INVENTOR. THOMAS JAMES,JR. BY

(UM M1 $202M ATTORNEYS June 10, 1958 T JAMES, JR 2,838,141

31G ROD MECHANISM SELF-ADJL'IS FOR RAIL BRAKE SYSTEM Filed May 12, 1954 9 Sheets Sheet 5 INVENTOR. THOMAS JAME$,JR. BY

2W4 w M ATTORNEYS June 10, 1958 T. JAMES, JR 2,833,141

" SELF-ADJUSTING R OD MECHANISM FOR RAILWAY BRAKE SYSTEM Filed May 12, 1954 9 SheetsSheet 6 Fig. I5

INVENTOR. 4 THOMAS JAMES JR.

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SELF-ADJUSTING ROD MECHANISM FOR RAILWAY BRAKE SYSTEM 9 Sheets-Sheet 7 Filed May 12. 1954 INVENTOR. THOMAS JAMES JR.

ATTORNEYS June 10, 1958 I T. SELF-ADJU JAMES, JR

2,838,141 STING ROD MECHANISM FOR RAILWAY BRAKE SYSTEM 9 Sheets-Sheet 8 Filed May 12. 1954 mom June 10, 1958 T. JAMES, JR 2,838,141

SELF-ADJUSTING ROD MECHA M FOR RAILWAY BRAKE SYSTE Filed May 12.- 1954 9 Sheets-Sheet 9 Unite insuflicient to set the brakes.

SELF-ADJUSTING ROD MECHANISM FOR RAILWAY BRAKE SYSTEM Thomas James, Jr., Philadelphia, Pa., assignor to Specialty Brake Appliance Company, Camden, N. 1., a corporation of New Jersey Application May 12, 1954, Serial No. 429,328

34 Claims. (Cl. 188-198) This invention relates to self-adjusting rod mechanism; more particularly,-to adjustable rod mechanism of a type particularly suitable for application to braking systems of railway vehicles to adjust for slack and has for an object the provision of a self-adjusting rod mechanism which is reliable in operation, of rugged construction, and which does not interfere with either automatic or manual application of the brakes regardless of the extent of movement required of the rod mechanism to .set the brakes.

As is well understood by those skilled in the art, the brakes on a railway vehicle are applied by the movement of a piston within a braking cylinder. The length of the cylinder necessarily limits the extent of movement of the piston and thus the extent of movement of the brake rod which may be produced by the piston in the application of the brakes. If the shoes of the brake Wear to a sufiicient extent, maximum movement of the piston will be Because of this problem, there have been proposed many schemes for automatically adjusting the brakes in order to compensate for wear of the brake shoes. However, such schemes leave much to be desired in reliability of operation, and particularly in leaving the braking mechanism free for the application of hand brakes notwithstanding the extent of wear on the brake shoes.

The present application is a continuation-in-part of my earlier filed application Serial No. 262,101, filed December 17, 1951, now abandoned, which is a continuation-inpart of my parent application Serial No. 161,349, filed May 11, 1950, now abandoned.

The present invention is particularly useful in connection with braking systems of the type known as the AB Freight Braking Equipment. In such equipment the brakes provided throughout the train are operated in response to change in the air pressure in the train pipe which extends the full length of the train. More particu larly, the engineman, in operating the brake-applying lever in order to apply the brakes, releases air from the train pipe. This reduction immediately extends throughout the length of the train pipe. In accordance with the manner in which the pressure in the brake pipe is reduced, an AB valve on each car operates to initiate at all the cars throughout the train the desired braking. As well understood by those skilled in the art, there is, upon initial reduction of brake pipe pressure, local venting of air from the train pipe at all brake locations. Air flows both from the train pipe and from each of the auxiliary reservoirs to each brake cylinder which moves the brake piston in brake-applying direction. When the brake pressure in the brake cylinder builds up to a predetermined value, for example, nine pounds, the AB valve closes the vent port from the train line. The brakes are then set for a predetermined braking action. The time required for building up that pressure will depend upon the volume to be filled in each brake cylinder.

From the foregoing it will be seen that different movements of'the piston within the cylinder will mean different tates atent O i 2,838,14l Patented June It), 1958 "ice volumes to be filled with air for the buildup of the brakecylinder pressure to the predetermined amount. Thus, if each brake cylinder requires a materially different movement for its piston to apply the brakes, there will be uneven or a slightly different air pressure in the brake pipe line from car to car, and the brakes will not be simultaneously set. There will not be simultaneous braking throughout all cars of the train. Hence, there will result a loss of uniform braking from car to car which means a loss of control of the train, with resulting damage due to the shocks which occur with uncontrolled slack inthe train. In accordance with the present invention, the volume within each brake cylinder to be filled with air at predetermined pressure is at all times maintained substantially uniform throughout all the cars of the train. There are avoided the foregoing variations in pressure in the brake pipe and there is assured uniform braking throughout all cars of the train.

Further in accordance with the invention, the features of my invention lend themselves to incorporation in an automatically adjustable rod assembly which is not only of unusual low cost but which assembly as a unit may readily replace the push rod and pull rod assemblies of existing braking systems greatly to improve over-all operation thereof.

In carrying out my invention, there is provided in a braking system having an actuator and associated brakeapplying linkage for moving brake shoes into and out of braking positions, brake-adjusting mechanism also sometimes referred to as slack-adjusting mechanism comprising adjustable members for varying the overall length thereof and included in the linkage between the actuator and the brake shoes. A length-controlling element is secured to one of the adjustable members and a lengthcontrolling element is supported in cooperating relation with the first length-controlling element. Operating mechanism is provided for the length-controlling elements including a lever pivoted to a movable part of the linkage. There is further provided a support normally engaged by an element of the operating mechanism for preventing relative movement between the support and the last-named element and for producing movement of the pivoted lever in one'direction only with each movement of the linkage toward brake-applying position. The lever and the lengthcontrolling elements are mechanically connected whereby movement of the second one of the length-controlling elements with the linkage during a brake-applying operation beyond a predetermined amount conditions the brakeapplying linkage toward brake-releasing position to change the length of the linkage in a direction to reduce slack in the brake-applying linkage in movement of the brake shoes toward a braking position.

Preferably, the first length-controlling element comprises a member having a plurality of teeth and the distance between adjacent teeth corresponds to a predetermined displacement of the actuator in the braking system.

More particularly, in carrying out the invention in one form thereof, there is provided a self-adjusting push rod assembly or mechanism having one end disposed in abutting engagement with the brake-applying piston. The opposite ends of the push rod assembly is pivotally connected to the live brake lever. The push rod assembly consists of two elongated members threadedly connected to each other, one of which is adjustable for varying the length of the assembly. A crosshead supported on one of the members has pivotally secured thereto an actuating lever such as a ratchet lever, one end of which has a stop rod slidable in a fixed member and forming a stop to prevent pivotal movement of the ratchet lever in one direction. Upon application of braking pressure, the piston presses against and moves the push rod assembly to actuate the live brake lever. If the brakes are applied after a predetermined displacement of the piston, the ratchet lever is ineffective to adjust the length of the push rod assembly. Any movement of the piston beyond the predetermined amount is effective in rotating the ratchet lever to bring into action a pawl and ratchet wheel. The latter are effective upon return movement of the piston to lengthen the push rod so that upon the next application of braking pressure, there will again be the predetermined piston displacement for application of the brakes. This self-adjusting feature of the push rod assembly compensates for any movement of the piston beyond the predetermined amount, whether occasioned by wear of the brake shoes or otherwise.

Further in accordance with the invention, the extent of adjustment of the push rod assembly is also predetermined, and in the event it is extended to a predetermined limit, the pawl and ratchet wheel are disengaged to prevent further lengthening of the push rod assembly. There is thus avoided possibility of damage to the adjusting mechanism which might otherwise occur.

The foregoing features do not interfere with manual application of the brakes regardless of wear of the shoes and regardless of the extent of movement required of the push rod assembly in order manually to set the brakes.

This is an important safety feature in the operation of the" train since it is important that there be manual means to set the brakes after brake-shoe wear beyond the limits of adjustment of the push rod and the maximum movement of the brake-applying piston.

Further objects and advantages of the invention will be pointed out in connection with the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a plan view, partly in section, of an embodiment of the invention applied to a brake cylinder;

Fig. 2 is a side elevation of Fig. 1;

Fig. 3 is a fractional perspective view, partly in section, of the crosshead and selected parts secured thereto;

Figs. 4, 5 and 6 are fractional plan views showing the ratchet lever and associated parts'in different'positions of operation;

Fig. 7 is an exploded perspective view, partly in section, illustrating the cooperative relation of the more important parts of the assembly;

Fig. 8 is a perspective view of the cross head with the parts shown in Fig. 3 removed;

Figs. 9 and 10 are fractional perspective views of one of the elongated members of the assembly;

Figs. 11-13 are sectional views taken on the line 1111 of Fig. 2 with the parts which automatically limit the extent of elongation of the push rod assembly shown in different positions;

Fig. 14 is a sectional elevation taken on the line 14-44 of Fig. 2 of the ratchet assembly;

Fig. 15 is a plan view of a modification of the invention particularly adapted to railway cars having brake mechanism of the two-lever type;

Fig. 16 is a sectional view of a self-adjusting rod included in the mechanism of Fig. 15;

Fig. 17 is a side elevation of a modification of the 'invention particularly adapted for use with brake systems of the three-lever type, such, for example, as are used on hopper cars;

Fig. 18 is a view taken on the line Eh-13 of Fig. 17;

Fig. 19 is a plan view of a further modification of the invention illustrated in connection with brake mechanism of the two-lever type and showing the parts in the brake applied position;

Fig. 20'is a sectional view taken along the lines 2029 in Fig. 19;

Fig. 21 is a section view taken through the pawl carrier 41A and similar to Fig. 22 but with the parts in brakereleased position;

Fig. 22 is a sectional view taken along the lines 22-22 1 the brakes.

'4 in Fig. 19 with the parts in brake-applied position where the piston travel does not exceed the minimum travel re quired for automatic adjustment;

Fig. 23 is a sectional View similar to Fig. 22 with the parts in brake-applied position where the piston travel exceeds the minimum travel required for automatic adjustment; and

Figs. 24 and 25 are sectional views, similar to Figs. 21-23, showing the parts in extreme positions during the resetting operation.

Referring to the drawings, the invention in one form has been shown applied to a brake cylinder it) secured by flange 10a to the frame of the under-carriage of a railway vehicle such as a freight car. Within cylinder 19 is a piston 11 biased to its right-hand position, as viewed in Fig. 1, by a coil spring 12 and operable in brakeapplying direction by entry of air through pipe 23. Within a protecting sleeve 14 secured to the piston 11 are two elongated members 15 and 16 forming essential parts of the automatically adjustable push rod assembly. The outer elongated member 15 is formed by sleeves interconnected by an internally threaded nut 15a receiving the threaded end of the inner eiongated member The right-hand cylindrical member or sleeve 15 includes a thrust bearing 15b which engages a slightly concave spherical surface of the piston 1 A substantial length of the inner member 16 is unthreaded and terminates in a yoke 16:: through which extends a pivot pin 17 interconnecting yoke 16a and the live brake lever 18. Thus, movement of the piston it to the left rotates the live brake lever 18 about the pivot pin 19 which is effective through lever 13 to control a set of brakes of one truck and is effective through a tie rod 2% and the cylinder dead lever 21 to control the application of a set of brakes of another truck. The brake lovers 2? and 21 and the tie rod 20 pivoted thereto by pins 19 and 1% are of standard construction known to those skilled in the art, further details of which need not be here forth.

In normal operation, a predetermined displacement of piston 11 from the disengaged or brake releasing position, as illustrated in Fig. 1, will be required to apply the brakes. If for any cause the piston 11 must be moved beyond a predetermined amount, as for example, eight inches, an adjusting mechanism is brought into play automatically to lengthen the push rod assembly so that upon the next application of braking pressure only the predetermined displacement of the piston is required to apply This mechanism includes an actuating lever such as a ratchet lever 25 pivoted intermediate its ends by pivot pin 26 to a crosshead 27 slidably supported on the inner unthreaded end member 16 which cannot rotate by reason of provisions which will later be explained. Pivotally secured to the lower end portion of ratchet lever 25, as by a pivot pin 28 extending through one of the selected openings therein, is a stop rod 29 having a shoulder 29a abutting against a stationary support 30 which may be welded, as shown, or otherwise secured to the non-pressure head of the brake cylinder. The stop rod 29 has an end of substantial length extending through an opening in the stationary support 3%, which opening is of a size materially greater than the cross-sectional area of rod 29.

As best seen in Figs. 2 and 7, it will be observed that the ratchet lever 25 is carried by one end of pivot pin 26 which extends through an opening in the crosshead 27, to the opposite end of which is secured a rocker arm 31 having a bifurcated end through which extends the pivot pin 32 pivotally to support a spring rod 33 which, as best shown in Figs. 3 and 7, extends downwardly through a rectangular opening in a shoulder or fixed spring seat 27:! formed integrally with the crosshead 27. The lower end of spring rod 33 has secured thereto a cross member 3 3 which supports a spring seat 35, a coil spring 36 having one end bearing against the lower surface of spring seat 27a and the other end of which bears against the seat 35 to bias downwardly the rod 33 and to bias the ratchet lever 25 for counterclockwise rotation to maintain the shoulder 29a against the fixeil support 30, Figs. 1 and 2.

Upon application of brake pressure to the piston 11, the push rod assembly as a whole will be moved to the left.' The left-hand member 15 has secured thereto a flange 37a forming a part of a ratchet wheel 37 rotatable relative to the inner member 16. The outer surface of the flange 37a is engaged by an arcuate extension 27b of crosshead 27 mechanically to interlock crosshead 27 with the tubular member 15 so that the crosshead 27 is at all times moved or carried with tubular member 15. Thus, as the crosshead 27 is moved to the left, the pin 26 moves with it. However, inasmuch as the spring 36 maintains the ratchet lever 25 with the shoulder or abutment 29a against the stationary stop or support 30, the movement of pin 26 rotates lever 25 about pin 28 lifting the opposite end of lever 25, as viewed in Figs. 1 and 7. In other words, there is rotation of ratchet lever 25 in a counterclockwise direction about pin 26.

The movement that takes place is illustrated in Figs. 4-6, Fig. 4 illustrating the parts in the same angular positions as in Figs. 1 and 7. In Fig. 5 the crosshead 27 'has been moved by an amount corresponding with the desired predetermined piston displacement for application of the brakes. It will be observed that the ratchet lever 25 has been rotated through approximately 60.

The rotation of ratchet lever 25 actuates through pin 38 extending through the yoke-shaped end 25a of lever 25, a pawl link 40, details of which are best seen in Fig. 7. As the pin 38 is moved upwardly it lifts pawl link 40, which in turn rotates a pawl-carrying housing 41 within which is pivotally mounted a pawl 42, detailed construction of which will be later described. The pawl 42 is rotated substantially to engaging position with a preceding tooth of ratchet wheel 37. If the piston exceeds its predetermined displacement, a slight amount beyond that shown in Fig. 5, the pawl 42 drops behind a preceding tooth preparatory to adjustment of the push rod assembly. The enlarged opening in support provides for the change in angular position of rod 29 which may be observed by comparing the position of rod 29 in Figs. 4 and 5 and also provides for lateral movement with the push rod assembly as a whole.

Assuming that the pawl has dropped behind the tooth of the ratchet wheel 37, then upon release of the brakes the weight of the brake assembly acts through brake levers 18, 21 and tie rod 20 to return the push rod assembly to the position shown in Figs. 1 and 4. During this return movement, the ratchet lever 25 is rotated from the position shown in Fig. 5 in a clockwise direction about pivot pin 28 carried by stop rod 29 to rotate the pin 38 downwardly, thus rotating the ratchet wheel 37 in a clockwise direction as viewed in Fig. 7 to rotate the nut or threaded member 15a in a clockwise direction about the threaded member 16. The elongated threaded member 16 cannot rotate, due to its connection by pivot pin 17 to the live brake lever 18. The rotation of the threaded member 1512 is in the direction to increase the length of the push rod assembly. Hence, when the thrust bearing 15b is again in engagement with the piston 11 and there is application of braking pressure, the push rod assembly, now longer than before, will rotate the live brake lever to brake-applying position with less movement of piston 11. Thus, upon the application of the brakes the piston willapply the brakes after attainment only of its predetermined displacement. This automatic adjusting action will continue whenever and so long as more than a predetermined piston displacement is required to apply the brakes, except as hereinafter explained.

It will be recalled that the spring 36 acting through the rocker 31 applies a bias to the ratchet lever 25 tending to rotate it in a counterclockwise direction, as viewed in Figs. 4-6. The spring 36 is strong enough so that upon the return movement of the push rod assembly in r 6 the brake-releasing direction, the pin 26 in moving from the position shown in Fig. 5 to the position shown in Fig. 4 is effective to rotate the ratchet lever 25 about the pin 28 to rotate the ratchet wheel 37 in a clockwise direction to effectuate the foregoing adjustment.

Brakes of the type under consideration in general include manual operating means which has been illustrated in Figs. 4-6 as including a relatively strong chain 43. It will be observed, Fig. 4, that if a pulling force be exerted on the chain 43 which is attached directly, as by a clevis, to the pin 17, the live brake lever 18 will be actuated, and at the same time the push rod assembly will be moved outwardly of the brake cylinder 10 but the piston 11 and its sleeve 14 with terminal flange 14a will not be moved. The ratchet lever 25 and its associated parts wiil function again to advance the ratchet wheel 37 one tooth each time the movement of the live brake lever 18 exceeds a rotation corresponding with that which would also be produced by the predetermined piston displacement, of say eight inches. Thus, the automatically operable self-adjusting push rod assembly is equally effective during application of the brake by air pressure or by hand to keep uniform the required piston travel for pneumatic braking.

In operation of trains, there has some times arisen conditions where because of wear of brake shoes or otherwise, braking by application of air pressure has been impossible; for example, by reason of a need of rotation ofthe live brake lever 18 beyond that which can be produced by the piston displacement which is limited by the length of the brake cylinder 10. Further in accordance with the present invention, the brakes may still be manually applied by continued operation of the hand brake which exerts, through chain 43 or other suitable mechanical connection, a continuing application of force to move the push rod assembly to the left to continue rotation of the live brake lever-18 in a brake-applying direction. For such abnormal operation of the brake, the self-adjusting push rod assembly of the present invention is designed not only to protect itself against disablement and injury but also as not to interfere with such abnormal movement necessary for brake application.

More particularly, the parts have been shown in Fig. 6 as operated by the hand brake to an abnormal braking position where the push rod assembly including the member 15 has greatly exceeded the maximum piston displacement within cylinder 10. However, the ratchet lever 25 does not move beyond the position shown in Fig. 6. After it attains that position, the stop rod 29 moves with ratchet lever 25, the end thereof sliding through the opening of the stationary support 30. In this manner there is avoided any possibility of the pin 28 being moved over-center with respect to a line interconnecting the pin 26 and the center of the opening through the stationary support 30. Were such over-center movement permitted, there would be interference in the return of the push rod assembly to the normal position of Fig. 4. Such over-center operation can never occur, however, due to the provision of a shoulder 33a, Figs. 3 and 7, on spring rod 33, which shoulder is moved by rocker arm 31 against the upper face of the spring seat 27a, thus removing the bias of spring 36 from ratchet lever 25, which spring bias has heretofore maintained stop rod 29 against its stationary support 3%. Thereafter, the assembly as a whole including stop 29 moves with the push rod assembly without further relative movement between it and ratchet lever 25. It will, of course, be understood that upon return movement of the push rod assembly to its normal position, the foregoing operations are reversed and the apparatus is again in readiness for further adjustment or operation of the brakes.

Now that the operation of the self-adjusting push rod assembly has been described with reference to several of its important advantages, attention will be directed to further aspects of constructional features. In' Figs; 3

and 8 there has'been illustrated in perspective the crosshead 27. The body of crosshead 27 is provided with a central opening 270 through which the inner member 16 extends. The inner member 16 is provided along its lower surface with an elongated slot 160 to receive an L-shaped key 45 pivoted by pivot pin 46 to crosshead 27 and extending into a recess 27d and upwardly for engagement with slot 16c of member 16. The key 45 prevents rotation of crosshead 27 relative to member 16 which, it will be recalled, is prevented from rotation by its connection to live brake lever 18.

The crosshead 27 has a semi-circular yoke 27b supported from arms 27c. It will be recalled the yoke 27b was earlier described as forming a mechanical interlock, the inner face of the yoke 27b being disposed behind the outer face of the flange 37a of the ratchet wheel 37. By providing a crosshead 27 of the shape illustrated in Figs. 8 and 3, the relatively movable parts are rigidly held together by the single casting forming the crosshead 27, a matter of great economy in manufacture and ruggedness in final product.

It will be observed that there is a cut-away section 27 adjacent keyway 27d and including a boss 27g having an opening to receive a pivot pin 47, Fig. 3, which carries a tripping member 48 having one end 43a extending upwardly into and having a shape complementary with that of the keyway 160 of the member 16. The tripping member 48 also is provided with a shoulder 43b which, in manner hereinafter to be explained, is effective to move the pawl 42 to an inactive position out of engagement with ratchet Wheel 37.

Referring to Figs. 9 and 10, it will be observed the keyway 160 of member 16 does not extend the full length thereof but terminates in an outwardly inclined surface adjacent the threaded portion, a side wall of rod 16 being cut away along the length of the outwardly inclined surface as indicated by reference character 16d. So long as the end 43a of tripping member 48 is Within keyway 16:, Fig. 11, it cannot move outwardly therefrom because of engagement with the sides of the keyway 160. However, after inner member 16 has been moved relative to member by an amount to bring the inclined end of keyway 160 against end 48a, tripping member 48 is rotated about pivot pin 47, the cut-away wall portion 16d freeing the end 48a for said pivotal movement out of keyway 160. The end 480, Fig. 12, then rests upon the cylindrical surface of rod 16, by means of which tripping member 48 is prepared to resist a substantial force to be applied thereto in manner now to be described. For clarity, the rod 16 in Figs. 9 and 10 has been illustrated with the keyway 16c extending upwardly, whereas, of course, in the assembled position it, as indicated in Figs. 11-12, extends downwardly.

In Fig. 11, the pawl housing 41 is illustrated in its normal position before movement of piston 11 in brakeapplying direction. During such movement of the piston, the pawl link 41} secured by pivot pin 49 to pawl housing 41 is moved upwardly by pin 38 which extends through the yoke a of ratchet lever 25, Figs. 4-6, thus rotating the pawl housing 41 in a counterclockwise direction about the axis of member 16, as viewed in Figs. 7 and 11-13. Pawl 42 functions, as described above, to adjust the member-16 relative to member 15. When the adjustment has continued to a point where the end of keyway Me has been reached, as by movement of rod 16in a direction through the plane of the paper, the tripping member 48 is moved to the position shown in Fig. 12 by the outwardly inclined end of keyway 16c, the cut-away wall portion shown at 16d permitting the pivotal movement about pivot pin 47. Thus, the shoulder 48b is moved into the path of a shoulder 51a of a pawl-releasing lever 51 which is secured to the pivot pin 52 to which the pawl 42 is secured as shown in Fig. 14.

Thus, as pawl housing 41 is rotated about the axis of member 16, the shoulder 51a engages shoulder 48b, as

illustrated in Fig. 13. However, since tripping member 48 is held in the position illustrated by the engagement of its end 48a with the cylindrical surface of member 16, the member 48a cannot rotate. However, continued movement of pawl housing 41 produces rotation of pawlreleasing lever 51 in a counterclockwise direction, thereby rotating pivot pin 52 and thereby rotating the pawl 42 out of engagement with the teeth of ratchet wheel 37. The pin 52 has a fiat face 52a which is engaged by a like flat face formed in pawl 42 and member 51. The pawl 42, with the pawl-releasing lever 51 in the position shown in Figs. 11 and 12 occupies the position illustrated in Fig. 14, an over-center coil spring 53 being effective to press a plunger 54 against a boss 42a of pawl 42 to bias the latter toward the teeth of ratchet wheel 37.

Counterclockwise rotation of pawl-releasing lever 51, as viewed in Figs. 11-13, likewise produces counterclockwise rotation of pawl 42, as viewed in Fig. 14, rotating the boss 42a through an over-center position to reverse the direction of the bias from plunger 54, thereafter to bias pawl 42 for rotation in the counterclockwise direction and away from ratchet wheel 37. It is required that there be manual operation of pawl release lever 51 to return pawl 42 to its first over-center position, where it will stay, providing new brake shoes have replaced the Worn-out ones.

From the foregoing, it will be seen that after a predetermined limit of adjustment has been attained by continued lengthening of the push rod assembly, the pawl 42 is automatically moved out of engaging relation with the ratchet wheel 37, and it is thereafter maintained out of engaging position. Since the pawl-releasing lever 51 is swung from its normal position, shown in Figs. 11 and 12, to the releasing position where it is maintained, it performs a useful signaling function which by its position informs inspectors that the limit of adjustment of the push rod assembly has been attained. It also serves the purpose of protecting against the possibility of the threaded end of member 16 from being fed beyond the threaded member or nut 15. The pawl-releasing lever 51 serves the further purpose of permitting manual operation at any time to move the pawl 42 to its inoperative position with respect to the ratchet wheel 37. This feature is of advantage in the original assembly of the mechanism and also for resetting the push rod assembly by rotation of member 16 to decrease the length of the push rod assembly, as for example, after installation of new brake shoes.

The ratchet Wheel 37, as has already been described, includes the outer flange 37a to which the outer member 15 is secured. Also formed integrally with the ratchet wheel 37 is an inner cylindrical portion 37b which forms a bearing surface for the pawl housing 41. The gear teeth are formed in an axially extending portion of the cylindrical part 3777. In Fig. 14 the larger diameter in one face of the pawl housing 41 is illustrated, while in Fig. 7 the smaller diameter opening in the opposite face is shown providing a bearing surface on member 16.

It is to be observed that the movement of the piston 11 needed to bring the pawl 42 behind a gear tooth may be readily adjusted by inserting the pin 28 into one or the other of the holes on the opposite side of the position shown in Figs. 4-6. Thus, a movement of the piston of six, eight, or ten inches, more or less, may be provided as desired to effect a lengthening adjustment of the push rod assembly.

The embodiment illustrated in Figs. 1-14 is particularly adapted for application to locomotives. The invention, however, is not limited to locomotive applications, the principles thereof fully explained above being equally applicable to brake mechanisms on railway cars, particularly freight cars.

As shown in Fig. 15, a brake cylinder having a piston, push rod, spring and push rod sleeve of the same type as shown inFig. l, is connected by pin 17 to a live brake lever 18,,a dead brake lever 21 being pivoted at 21a to a stationary support. Instead of locating the adjustable telescopic members iii place of the push rod as in the modification of Figs. 1-14, the adjustable telescopic members in Fig. comprise the tie rod A of Fig. 15. Thus one end of tie rod 20A is connected to the dead brake lever 21, by a yoke 101 and pivot pin 102. A rod 103 has one end threaded into yoke 101 and pinned as at 104 or welded to the yoke 101, Fig. 16. Secured near the opposite end of the rod, as by welding, is a bearing 105 over Which there slides a sleeve 106. To the left of thebearing 105 the end of rod 103 or the inner member of the telescopic assembly is threaded and extends through a nut 107 welded to a sleeve 108 which is also welded to sleeve 106. The sleeve 108 is welded to the flange 37a of the ratchet wheel 37, the construction being the same as in the modification of Figs. 1-14. However, the ratchet wheel 37 is carried by a shaft 109 formed by a bolt having a head 110 and an end 111 of reduced section threaded into and pinned or welded to a yoke 112 which is in turnpivoted as at 113 to the livelever 18. A pawl housing 41 and the internal construction thereof including the ratchet wheel and pawl are identical with the previous modification and as shown in Fig. 14, the only difference being that the parts 27e of the crosshead are not used in the modification of Fig. 16 and the short shaft 109 replaces the inner member 16 of the foregoing modification. Thus, if the pawl-carrying housing 41 be rotated in a direction .to move the pawl 42, Fig. 14, to the next adjacent tooth, it will be seen that the ratchet wheel 37 will be rotated carrying with it the sleeve 108 and the nut 107 relatively to adjust the length of the telescopic members. In the modification of Figs. 15 and 16 the rotation of the nut 107 is in a direction to shorten the length of the rod between pivot. pins 113 and 102, whereas in the previous modification the efiect of operation of the pawl Was-to lengthen the push rod.

The rotation of the pawl-carrying housing 41 is accomplished in manner similar to the preceding modification, that is to say, the ratchet lever is pivoted intermediate its end as by a pin 26 which in Fig. 15 is carried by the push rod 117 or the yoke secured to the end thereof. To one end of the ratchet lever 25 there is pivotally secured, as at 28, a stop rod 29 which extends through and is slidably supported by the stationary stop 30. A Washer 29a is welded to the stop rod 29 and other washers 29b are provided to adjust the length of the rod between pivot 28 and stop 30. A spring 120 has one end bearing against stop and the opposite end bearing against a washer 121 held in place by a nut 122 threaded on the end of stop rod 29. The spring 120 acts in the direction to maintain the washers 2% against stop 30. Upon movement of the live brake lever 18 in a brake-applying direction whether by the chain 43 (manual operation) or by the actuator 100, as by application of air to the piston thereof, the pin 26 carried by push rod 117 moves in a left-hand direction as viewed in Fig. 15. The ratchet lever 25, pivoted at 26 and having its lower end as at pivot 28 held stationary as by spring 120, operates as a crank to rotate the opposite end thereof pivotally connected as by pivot pin 118 to a link 119 to raise, as viewed in Fig. 15, the pawl-carrying housing 41. The direction of rotation of the pawl housing 41 moves the pawl towards a-preceding tooth. If before engagement of the brake shoes with the wheels through actuation of rods 120 and 121, the pin 26 is moved to the left beyond a predetermined amount, the pawl 42 (Fig. 14) engages a preceding tooth of the ratchet wheel 37. Upon release of the brakes the return movement of pin 26 rotates the ratchet lever 25 again operating as a crank with the lower end held stationary by the abutment of the washer 2% against stop 30 to rotate the pawl and ratchet wheel in thereverse direction to shorten the length of the tie rod 20A by a predetermined amount. This action will continue whenever the brakes 75,

10 require adjustment and until the brakes are applied by a predetermined movement of the actuator 100 including the push rod 117. Accordingly, it will be seen that in this modification, as well as in the preceding one, the required movement of a piston within the brake cylinder is maintained at a predetermined fixed amount to apply the brakes so long as there remains enough of the brake shoe to insure a braking action, the automatic brake adjustor including the tie rod 20A compensating at all times for wear of the brake shoes and maintaining constant a predetermined piston displacement for application of the brakes.

When new brake shoes are applied, the pawl 42 (Fig.

14) may be, manually rotated by a pawl releasing lever 51 (Fig. 13), not shown in Figs. 15 and 16. After release of the pawl from the ratchet wheel 37, the sleeves 106 and 108 may be rotated to lengthen the tie rod 20A as much as may be necessary and generally to the initial position illustrated in Fig. 16.

The braking system illustrated in the modification of Figs. 1-14 and the braking system of the modification of Figs. 15-16 are of the two-lever type, that is to say, systems including a live brake lever 18 and a dead brake lever 21. There are also in use three-lever braking systems such as those used on hopper cars. In applying the present invention to a three-lever brake system (Figs. 17 and 18) the arrangement including the ratchet lever 25, stop rod 29 and the link 119 used for rotating the ratchetcarrying housing 41 are identical with the modification of Figs. 15-16. However, in the modification of Figs. 17 and 18 the live brake lever has its upper end pivoted to a stationary support, an intermediate portion thereof being pivotally connected as by a pin 17 to the end of the push rod 117. To the lower end of the live brake lever 150 there is pivotally secured, as by pin 151, a connecting rod 152 which at its other end is connected as by pin 153 to a floating brake lever 154, which at its lower end (not shown) is connected to the brake-applying truck levers (not shown). Intermediate the ends of the floating lever 154 and connected at one end by the pin 155 is an adjustable rod 20A of construction identical with that already described in connection with Figs. 15 and 16. This rod 20A is connected at its other end as by a pin 156 to a lever 157 pivoted at its lower end to a stationary support (not shown) and connected as by pin 158 atits upper end to a brake-applying truck lever 159.

Upon applying the brakes either by the actuator 100 or as by hand by chain 43, the ratchet lever 25 is rotated in manner already described and through link 119 operates through crank arm 160 pivoted on pin 151 to move a link 161 to rotate through crank arm 162 pivoted on pin 153 the pawl-carrying housing 41, the link 164'extending between the housing 41 and the crank 162 and the link 161 being pivotally connected at 163 to crank 162 for universal movement. Thus if the movement of the push rod 117 exceeds a predetermined amount the rod 20A is shortened for application of the brakes with less movement on the part of the actuator 100.

Referring to Fig. 19, there is shown a further modification of the invention wherein the adjustable 1ength-controlling device comprises a pull-rod or tie-rod assembly 20B similar to the tierod assembly 20A of Fig. 15. In this modification, the brake cylinder 100 is provided with a piston, push rod, spring and push-rod sleeve of the same type as shown in Fig. 1, the push rod 117 being connected by pin 17 to the cylinder lever or live'brake lever 18 and the dead brake lever 21 being pivoted at 21a to a stationary support. The various parts in Fig. 19 have been shown with the brake in the applied position. The brake cylinder piston has traveled a distance just short of the position at which take-up occurs, such distance corresponding to a predetermined set value, such for example, as an 8-inch travel of the piston.

As may be. seen in Fig. 19, the pull-rod or tie rod assembly 20B is pivotally connected to levers 18 and 21 atv its end. by corresponding pins 113 and 102.. The pullrod assembly 2013 replaces the conventional pull-rod that normally interconnects the live brakelever 18 with the dead brake lever 21 and comprises a pair of members adjustable as to length in the form of telescoping members including an outer housing member 193A and an inner rod member 103A. One end of rod 103A is threaded into a yoke 101A and pinned at 14A or welded to the yoke 101A, the latter being pivoted on the dead brake lever 21 at a pivot 102. The opposite. end of rod 103A is provided with a screw section i658 which is adapted to be threadedly engaged by a nut portion 107A within the outer member 198A of the telescopic assembly. As illustrated, the nut portion 1ti7A preferably is formed integrally with the housing member 108A. An extension 108B. is provided for housing 163A to completely enclose and protect the screw section 103B. The housing mem ber 108A is supported for rotation about its longitudinal axis by bearing surface 108C, Fig. 20, the latter being carried by yoke 112A which in turn is pivoted at 113 on live brake lever 13. The bearing surface 108C is maintained in position against longitudinal movement relative to yoke member 112A through the cooperation of an external shoulder on housing 108A and a lock nut 170 threaded to the outer end of housing 108A. This will be seen that the housing member 108A is free to rotate about its longitudinal axis on hearing 108C and on the screw section 10313 of rod 103A to change the overall lengthof tie-rod assembly B.

For rotation of housing 108A there is provided on its outer surface adjacent its bearing NSC a plurality of ratchet teeth forming a ratchet wheel 37A the teeth of which are adapted to be engaged by a double-headed pawl member 42A. The pawl member 42A is pivotally carried by a pivot pin 52A which in turn is pivotally supported by a pawl carrier 41A, the latter being supported for rotation relative to housing member 108A.

To impart movement to pawl carrier 41A, there is pivotally carried on push rod 117 a ratchet lever 25A at pivot 26A. The ratchet lever 25A preferably is L-shaped and its short arm is connected to the pawl housing 41A by way of pivot pin 118, ratchet-lever connecting rod119, pin 125, pawl link A and pin 52A, the latter pin and link being'integral. The other arm of ratchet lever 25A is provided with a ratchet-lever pin 28A which pivotally engages a ratchett-lever guide rod or stop rod 29A The stop rod 29A comprises two sections 293 and 29Cinterconnected by a pivot pin 171. Section 290 is held against a, fixed support 30A by means of a coil spring 126 surrounding member 2913 and disposed between stop 39A and nut 122A. The section 29C is provided with two stop-shoulders 173 and 174, as later to be described.

As previously pointed out the parts in Fig. 19 have been shown in the brake-applied position. In the normal or brake-released position the push rod 117 is disposed within the brake cylinder 100 in fully retracted position and the pin 17 as well as the pivots 26A and 118 for ratchet lever 25A are in their right-hand positions as illustrated in phantom in Fig. 19. The location of the upper ratchet-lever pin 28A remains the same for both the brake-applied and brake-released" positions. When thebrake is applied, the push rod 117 moves to the left to the full line position shown in Fig. 19 and since ratchet lever, 25A is carried by push rod 117 at pivot 26A, the ratchet lever 25A, is caused to rotate about pivot 26A in a clockwise direction. This rotational movement is imparted to the pawl carrier 41A by way of the ratchetlever connecting rod 119, with the pawl carrier 41A being rotated in a clockwise direction about ratchet wheel 37A as viewed in Fig. 21. The pawl 41A at the end of. the brake application assumes the position shown in Big. 22

if the brake cylinder piston travel did not exceed thepredetermined distance, for example, eight inches, and the pawl member 42Alikewisewill he. in the position shown in Fig. 2.2 resting on top of tooth 37A". When the brake is released the push rod 117 is retracted with the brake cylinder piston and the pivot 26A for the ratchet lever 25A returns to its normal position indicated by the right-hand position of pivot points 26A and 118 shown in phantom. The pawl carrier 41A also returns to its brake-released position as shown in Fig. 21 with pawl 42A against the preceding tooth 37A. It will be observed that the ratchet wheel 37A of housing 108A does not rotate while the brake is being applied. The only time there is rotation of the ratchet wheel 37A and the housing 163A is when the brake is released and returns to its normal position and then there is only rotation if the piston travel exceeded the predetermined travel of eight inch-2s. if the piston travel did not exceed eight inches no takeup will result since the pawl carrier 41A and the pawl 42A will return to their positions as shown in Fig. 21 and the pawl 42A has not moved into driving engagement with a different tooth on the ratchet wheel 37A.

Upon a subsequent application of the brakes, if the piston travel exceeds eight inches, the pawl carrier 41A and the pawl 42A will be rotated to the positions shown in Fig. 23 with pawl 42A positioned for driving engagement with a different tooth 37A". Under these conditions when the brake is released the pawl 42A engages ratchet tooth 37A" and while returning to the brake-released position the pawl 42A will rotate the ratchet wheel 37A in a counterclockwise direction a fraction of a revolution thereby shortening the length of the pull-rod assembly 2013. in the modification illustrated in Figs. 1925, the ratchet wheel 37A comprises seven teeth and thus when pawl 42A advances one tooth there will be rotation of the-ratchet wheel 37A and the housing 1433A corresponding to one-seventh of a revolution. In a specific application, rotation of the housing 108A of the one-seventh of a revolution shortened the length of the pull-rod assembly 298 by approximately & inch.

As illustrated, Figs. 21 and 22, rotation of the pawl carrier 41A by an amount of approximately 51, from the position shown in Fig. 1, corresponds to the normal rake cylinder travel of eight inches. A rotation of more than about 53 is necessary before pawl 42A will engage exceeds its normal amount and thus there is eliminated any danger of a short travel take-up. As previously pointed out the take-up or slack adjustment occurs only when the brake rigging is not under tension, that is, when the brake cylinder is moving from the brakeapplied to the brake-released position, and thus the power required to adjust the length of the pull-rod assembly ZQB is very small.

It will be observed that the pawl 42A is of the double finger type and is provided with a flat surface 423. The pawl pin 52A is provided with two fiat surfaces 523 and 52C angularly disposed with respect to each other for independent cooperation with surface 428 to limit the relative rotation of pawl 42A. with respect to pin 52A. However, the fiat surfaces 42B, 52B and 52C have no effect during the automatic operation of the slack adjuster and their sole purpose is to permit resetting of the slack atjuster when brake shoes are replaced. During normal operation of the slack adjuster the pawl member 42A is free to rotate about the pawl pin 52A within prcdetermined limits established by the engagement of flat surface 425 with either of the fiat surfaces 523 or 52C. In the particular application illustrated in Figs. 19-25 the pawl member 42A is free to rotate about 27 on each side of a vertical plane passing through the rotational axis of hcusing'ltit A.

To. replace the brake shoes, section 29C of stop rod ratchet-lever pin 28A from its corresponding slot 29D in the stop rod 29A. It will, of course, be understood that at this time the brake is in the brake-released position. With ratchet-lever pin 28A disengaged from slot 29D, the ratchet-lever 25A can now be pivoted manually about pivot 26A with ratchet-lever pin 28A moving between stops 173 and 174 located on the guide section 29C of stop rod 29A.

In order to lengthen the pull-rod assembly 2013 so that the brake shoes can be replaced, it is necessary to reverse the action of the fingers of pawl member 42A on ratchet wheel 37A from' the positions shown in Figs. 21-23. To accomplish this the ratchet-lever 25A is moved to the extreme left in Fig. 19, compressing the spring 120 whereby there will be greater rotational movement of pawl carrier 41A in a counterclockwise direction than during the automatic operation previously described. As one pawl carrier 41A is rotated to the posi tion shown in' Fig. 21 by pawl link 40A and pin 52A, the flat surface 423 on pawl 42A engages the flat surface 52B on pin 52A. Upon further upward movement of pin 52A, by pawl link 40A, to the position shown in Fig. 24 there is concurrently further counterclockwise rotation of pawl carrier 41A. Since the flat surfaces 42B and 52B are already in engagement, the further rotation of pawl carrier 41A causes the pawl member 42A to compress spring 53A and move from the over-center position with respect to spring 53A as shown in Fig. 21 to another overcenter position as shown in Fig. 24. Thus the action of the two pawl fingers is reversed on ratchet wheel 37A. With pawl member 42A in the latter position, the ratchet lever 25A may now be moved between stops 173 and 174 for rotation of ratchet wheel 37A and housing 108A in a clockwise direction to lengthen the pull-rod assembly 20B. The ratchet lever 25A is moved back and forth between stops 173 and 174 until sufficient clearance is available to apply the new brake shoes.

After application of the new brake shoes, the ratchet lever 25A is moved toward the brake cylinder 100 as far as it will go, rotating the pawl carirer 41A to the position shown in Fig. 25, bringing flat surfaces 423 and 52C into engagement, which reverses the over-center position of the pawl member 42A and its fingers to normal automatic slack adjusting position with relation to the pawl pin 52A. The ratchet-lever 25A is then moved back until the ratchetlever pin 28A again becomes engaged with slot 29D on the guide section 290 of stop rod 29A. If excessive piston travel results after application of the new brake shoes this can be corrected by disengaging ratchet lever 25A from guide section 29C and moving the ratchet lever 25A back and forth between stops 173 and 174 until the correct piston travel is obtained. The ratchet-lever pin 28A is then reengaged with the slot 29D as shown in Fig. 19 and the slack adjuster is again ready for automatic operation.

While preferred embodiments of the invention have been disclosed, it is to be understood modifications may be made, and certain features used without other features, all within the scope of the appended claims.

What is claimed is:

1. A self-adjusting push rod assembly comprising a pair of elongated members threadedly connected for axial adjustment, a crosshead supported on one of said members, a ratchet lever pivotally supported from said crosshead, a stop rod having one end pivoted to one end of said ratchet lever, a stationary support normally engaged by said stop rod for limiting the movement of said stop rod in one direction only, movement of said crosshead rotating said ratchet lever about its pivotal support, a ratchet wheel carried by one of said elongated members for rosaid ratchet wheel upon predetermined movement of said crosshead, and a spring biasing said ratchet lever for rotation in a direction to maintain said stop rodagainst its stationary support.

2. A self-adjusting push rod assembly comprising a pair of concentric elongated members threadedly connected for axial telescopic adjustment, a crosshead slidably supported on the inner one of said members, a ratchet lever pivotally supported from said crosshead, a stop rod having one end pivoted to the lower end of said ratchet lever, means including a stationary support normally engaged by said stop rod for limiting the movement of said stop rod in one direction only, said outer one of said members engaging said crosshead to move it and to rotate said ratchet lever about its pivotal support, a ratchet wheel secured to said outer elongated member for-rotating it relative to said inner member, a pawl, means rotatably supporting said pawl for movement relative to said ratchet wheel, means interconnecting said rotatable support, for said pawl and an upper end of said ratchet lever for movement of said pawl into tooth-engaging position with said ratchet wheel upon predetermined movement of said elongated members, and a spring biasing said ratchet lever for rotation in a direction to maintain said stop rod against its stationary support.

3. A self-adjusting push rod assembly comprising a pair of elongated members threadedly connected for axial adjustment relative to each other, a crosshead supported by one of said members, aratchet lever pivotally suptating it relative to the other of said members, a pawl,

means pivotally supporting said pawl for movement relative to said ratchet wheel, means interconnecting said ported from said crosshead, a stop rod having one end pivoted to an end portion of said ratchet lever, means including a-stationary support normally engaged'by said stop rod for limiting the movement of said stop rod in one direction only, a spring biasing said ratchet lever for rotation in a direction to maintain said stop rod against its stationary support, movement of said crossheat rotating said ratchet lever about its pivotal support, a ratchet wheel carried by one of said elongated members for rotating it relative to the other of said members, a pawl, means pivotally supporting said pawl for movement relative to said ratchet wheel, means interconnecting said pivotal support of said pawl and said ratchet lever for movement of said pawl into tooth-engaging position with said ratchet wheel upon predetermined movement of said assembly, means including an over-center spring biasing said pawl in one over-center position into tooth-engaging position, and means for actuating said spring upon movement of said pawl from said one overcenter position to another over-center position for holding said pawl out of tooth-engaging position with respect to said ratchet wheel.

4. A self-adjusting push rod assembly for air brakes comprising a pair of elongated members adjustably connected for axial movement with respect to each other for varying the over-all length thereof, a crosshead supported on one of said members, an actuating lever pivotally supported from said crosshead, a stop rod having one end pivoted to an end portion of said actuating lever, means including a stationary support normally engaged by said stop rod for limiting movement of said stop rod in one direction only, and a spring assembly biasing said actuating lever for rotation in a direction to maintain said stop rod against its stationary support, said stop rod being free for bodily movement with said spring away from said stationary support, movement of said crosshead with said push rod assembly rotating said actuating lever about its pivotal support, and adjusting means operable by said 15 amount to remove the bias of said spring assembly from said actuating lever.

'6. The Combination set forth in claim 5 in which said stop rod has a shoulder normally engaging said stationary support and an end of said stop rod extending through said stationary support for a substantial distance permitting movement of said crosshead, said actuating lever, and said spring assembly with said elongated members to abnormal positions and for return thereof to normal positions.

7. The combination set forth in claim 4 in which one of said elongated members is provided with a keyway of predetermined length, a pivoted tripping member having one end extending into said keyway, said keyway being shorter than said one elongated member and shaped at one of its ends for actuation of said tripping member from said keyway upon movement of the end of said keyway beneath said tripping member, and means operable by said tripping member for disabling said adjusting means to prevent further relative adjustment between said elongated members.

8. The combination set forth in claim 7 in which said spring assembly includes a link having a shoulder and is connected to said actuating lever through said link, said shoulder being movable against :a stationary stop by rotation of said actuating lever beyond a predetermined amount to remove the bias of said spring assembly from said actuating lever.

9. The combination set forth in claim 4 in which one of said elongated members is provided with a keyway of predetermined length, a pivoted tripping member having one end extending into said keyway, said keyway being shorter than said one elongated member and shaped at one of its ends for actuation of said tripping member from said keyway upon movement of the end of said keyway beneath said tripping member, said tripping member having an end-portion fitting said keyway for retention of the same therein by the side walls thereof, said keyway having a cut-out portion of a side wall adjacent said end of said keyway for outward movement therethrough of said end-portion of said tripping memher, and means operable by said tripping member for disabling said adjusting means to prevent further rela- 'tive adjustment between said elongated members.

10. A self-adjusting push rod assembly for air brakes comprising a pair of elongated members relatively adjustable one with respect to the other, means including a pawl rotatable about the axis of said members to adjust the overall length of said members, one of said elongated members having a keyway of predetermined length and shorter than the length of said one of said elongated members, a pivoted tripping member with respect to which said keyway is relatively movable having its free end ext-ending into said keyway and normally retained therein by the side walls thereof and operable out of said keyway as the end thereof is moved beneath said tripping member, said keyway having a predetermined shape adjacent its end including a cut-away wall portion for pivotal movement of said tripping member outwardly thereof, and means operable upon movement of said tripping member out of said keyway for moving said pawl to an inactive position to prevent further relative adjustment between said elongated members.

ll. The combination set forth in claim 10 in which said pawl is biased to a member-adjusting position by a spring, said pawl being pivoted and having a portion movable with respect to said spring from one over-center position to another to reverse the rotational bias of said spring on said pawl, said means operable upon movement of said tripping member being effective to rotate said pawl from one over-center position to another over-center position, one of said over-center positions of said pawl is an inactive position to prevent further relative adjustment between said elongated members.

12. The combination set forth in claim 10 in which said pawl is biased to a member adjusting position by a spring, said pawl being pivoted and having a portion movable with respect to said spring from one over-center position to another to reverse the rotational bias of said spring on said pawl, said tripping member being provided with a handle for manual operation of said pawl from one over-center position to the other, one of said overcenter positions of said pawl is an inactive position to prevent further relative adjustment between said elongated members.

13. A self-adjusting push rod assembly comprising elongated members threadedly connected together for relative adjustment axially one With respect to the other, a pivoted tripping lever, one end of said lever and one of said elongated members respectively having mechanically interlocking structures including a recess and a projection, the interlocking structure of said elongated member extending axially thereof for a predetermined distance and terminating in an inclined surface for rotating said tripping member about its pivotal support, and ratchet mechanism carried by one of said elongated members including a pawl for rotating one of said elongated members relative to the other to adjust the overall length of said members, said tripping member engaging said pawl upon movement about its pivot for actuation of the same out of driving engagement to prevent further adjustment of the length of said push rod.

14. A self-adjusting push rod assembly comprising elongated members threadedly connected together for relative adjustment axially one with respect to the other, means for preventing rotation of one of said members comprising a pivoted tripping lever, one end of said lever and one of said elongated members respectively having mechanically interlocking structures including a recess and a projection, the interlocking structure of said elongated member extending axially thereof for a predetermined distance and terminating in an inclined surface for automatically rotating said tripping member about its pivotal support, ratchet mechanism carried by one of said elongated members including a ratchet wheel and a pawl for rotating one of said elongated members relative to the other to adjust their overall length, said tripping member engaging said pawl upon movement about its pivot for actuation of said pawl out of driving engagement with said ratchet wheel to prevent further adjustment of the length of said push rod, and means biasing said pawl into engagement with said wheel and after actuation by said lever for biasing said pawl to said position out of driving engagement with said wheel.

15. A self-adjusting push rod assembly for air brakes comprising a pair of elongated members adjustably connected for axial movement with respect to each other for varying the overall length thereof, a crosshead supported on one of said members, an actuating lever pivotally supported from said crosshead, a stop rod having one end pivoted to an end portion of said operating lever, means including a stationary support for limiting movement of said stop rod in one direction only, a spring assembly including a spring rod biasing said actuating lever for rotation in a direction to maintain said stop rod against its stationary support, said stop rod being free for bodily movement with said spring assembly and crosshead away from said stationary support, movement of said crosshead rotating said operating lever about its pivotal support, and means including a ratchet mechanism operable upon rotation of said operating lever for relatively adjusting said elongated members to change the length thereof after rotation of said operating lever by a predetermined amount, one of said elongated members having a flange, said crosshead having a circular portion behind said flange mechanically to interlock said crosshead and said flange, said ratchet mechanism being disposed between said crosshead and said flange.

16. In an automatic braking system having an actuator and an associated brake-applying linkage for moving abnormal braking position, the improvement of brakeadjusting mechanism comprising a pair of concentric elongated members threadedly connected for axial telescopic adjustment for varying the overall length of the linkage between the actuator and the brake shoes, a ratchet wheel secured to one of the elongated members, means for preventing rotation of the other of the elongated members, a pawl, means rotatably supporting said pawl for movement relative to said ratchet wheel, ratchetoperating mechanism including a ratchet lever pivoted to the actuator and movable therewith with movement of the actuator from a brake-releasing position to a brake-applying position, a stop rod having one end pivotally connected to said ratchet lever in spaced relation with its pivotal connection to a movable part of the linkage, means including a support in spaced relation with said ratchet lever slidably supporting said stop rod in normal engagement with said support preventing relative movement of said rod with respect to said support in one direction and preventing movement of said stop rod relative to said support in the opposite direction during a predetermined movement of the linkage in a brakeapplying direction to control rotation of said ratchet lever, said last-named means including yieldable means normally maintaining said stop rod in engagement With said support during automatic operation of the braking system and permitting movement of said stop rod away from said support during manual operation of the braking system to an abnormal braking position to increase the efiective length of said stop rod, and mechanical connecting means extending between the other end of said ratchet lever and said pawl, the disposition of the pivotal support of said ratchet lever and the pivotal connections thereto of said stop rod and of said mechanical connecting means producing during brake-applying movement of the linkage relative movement of said pawl relative to said ratchet wheel, movement of the linkage in a brake-applying direction only beyond a predetermined amount being eflective to move said pawl into a tooth-engaging position with said ratchet wheel, said ratchet-operating mechanism upon movement of the brake-applying linkage towards brake-releasing position rotating said pawl and said ratchet wheel in a direction to change the overall length of said telescopic members in a direction to decrease the extent of movement of the actuator necessary to move the brake shoes into their braking position.

elongated members threadedly connected for axial telescopic adjustment for varying the overall length thereof and included in the linkage between the actuator and the brake shoes, a ratchet wheel secured to one of the elongated members, the linkage including means for preventing rotation of the other of the elongated members, a pawl, means rotatably supporting said pawl for movement relative to said ratchet wheel, ratchet-operating mechanism including a ratchet lever pivoted to the actuator and movable therewith with movement of the actuator from a brake-releasing position to a brake-applying position, a stop rod having one end pivotally connected to said ratchet lever in spaced relation with its pivotal connection to a movable part of the linkage, means including a support in spaced relation with said ratchet lever slidably supporting said stop rod in normal engagement with said support preventing relative movement of said rod with respect to said support in one direction and preventing movement of said stop rod relative to said support in the opposite direction during a predetermined movement of the linkage in a brake-applying direction to control rotation of said ratchet lever, said last-named means including yieldable means normally maintaining said stop rod in engagement with said support during automatic operation of the braking system and permitting movement of said stop rod away from said support during manual operation of the braking system to an abnormal braking position to increase the effective length of said stop rod, mechanical connecting means extending between the other end of said ratchet lever and said pawl, the disposition of the pivotal support of said ,ratchet lever and the pivotal connections thereto of said stop rod and of said mechanical connecting means producing during brake-applying movement of the linkagerelative movement of said pawl relative to said ratchet wheel, movement of the linkage in a brake-applying direction only beyond a predetermined amount being effective to move said pawl into a tooth-engaging position with said ratchet wheel, said ratchet-operating mechanism upon movement of the brake-applying linkage towards brakereleasing position rotating said pawl and said ratchet wheel in a direction to change the overall length of said telescopic members in a direction to decrease the extent of movement of the actuator necessary to move the brake shoes into their braking position, and releasable means for moving said pawl to an inoperative position with respect to said ratchet wheel to permit axial telescopic adjustment of said concentric elongated members in reverse direction to vary the overall length thereof for resetting said brake-adjusting mechanism to its initial position for the installation of new brake shoes.

18. Inan automatic braking system having an actuator and associated brake-applying linkage for moving brake shoes into and out of braking positions, said actuator including a piston for power operation of the braking system to a normal braking position, and means manually operable for operating the braking-system to an abnormal braking position, the improvement of brake-adjusting mechanism comprising a pair of concentric velongated members threadedly connected for axial telescopic ad-- justment for varying the overall length thereof and included in said linkage between said actuator and said brake shoes, a ratchet wheel secured to one of said elongated members, said linkage including means for preventing rotation of the other of said elongated mem-' bers, a pawl, means rotatably supporting said pawl for movement relative to said ratchet wheel, ratchet-operating mechanism includinga ratchet lever pivoted intermediate its ends to the actuator, a stop rod having one end pivotally secured to one end of said ratchet lever, a,

support slidably supporting and engageable by said stop rod for limiting movement thereof in one direction only, and a mechanical connection extending between the other end of said ratchet lever and said pawl, movement of said ratchet lever with said linkage during a brake-applying operation rotating said pawl relative to said ratchet wheel, movement of said linkage beyond a predetermined amount being effective to move said pawl into a toothengaging position with said ratchet wheel, said ratchetoperating mechanism including a spring biasing said ratchet lever in a direction to maintain said stop rod v19 support during manual operation of the braking system to an abnormal brakingv position to increase the effective length of said stop rod.

19. In an-automatic braking system of the two-lever type having an actuator and an associated brake-applying linkage for moving brake shoes into and out of braking positions including a live brake lever pivotally connected to and movable with said actuator and a dead brake lever pivotally carried by a fixed support, said actuator including a piston for power operation of the braking syst-em to a normal braking position, and means manually operable for operating the braking system to an abnormal braking position, the improvement of brakeadjusting mechanism comprising a pair of concentric elongated members threadedly connected for axial telescopic adjustment for varying the overall length thereof and interconnecting the brake levers between the actuator and the brake shoes, a ratchet wheel secured to one of the elongated members, means carried by one of the brake levers for preventing rotation of the other of the elongated members, a pawl, means rotatably supporting said pawl for movement relative to said ratchet wheel, ratchet-operating mechanism including a ratchet lever pivoted intermediate its ends to the actuator and movable therewith with movement of the actuator from a brake-releasing position to a brake-applying position,

a stop rod having one end pivotally connected to one end of said ratchet lever is spaced relation with its pivotal connection to the actuator, means including a support in spaced relation with said ratchet lever slidably supportingsaid stop rod preventing relative movement of said rod with respect to said support in one direction and preventing movement of said stop rod relative to said support in the opposite direction during a predetermined movement of said linkage in a brake-applying direction to control rotation of said ratchet lever, said last-named means including yieldable means normally maintaining said stop rod in engagement with said support during automatic operation of the braking system and permitting movement of said stop rod away from said support during manual operation of the braking system to an abnormal braking position to increase the effective length of said stop rod, and mechanical connecting means extending between the other end of said ratchet lever and said pawl, the disposition of the pivotal support of said ratchet lever and the pivotal connections thereto of said stop rod and of said mechanical connecting means producing during brake-applying movement of the linkage relative movement of said pawl relative to said ratchet wheel, movement of the linkage in a brake-applying direction only beyond a predetermined amount being effective to move said pawl into a tooth-engaging position with said ratchet wheel, said ratchet-operating mechanism upon movement of the brake-applying linkage towards brakereleasing position rotating said pawl and said ratchet Wheel in a direction to decrease the overall length of said telescopic members interconnecting the brake levers to decrease the extent of movement of the actuator necessary to move the brake shoes into their braking position.

20. In an automatic braking system of the three-lever type having an actuator and associated brake-applying linkage for moving brake shoes into and out of braking positions including a live brake lever pivotally connected to and movable with said actuator, a dead brake lever pivotally carried by a fixed support and a floating brake lever disposed therebetween, said actuator including a piston for power operation of the braking system to a normal braking position, and means manually operable for operating the braking system to an abnormal braking position. the" improvement of brake-adjusting mechanism comprising a pair of concentric elongated members threadedly connected for axial telescopic adjustment for varying the overall length thereof and interconnecting the floating lever and the dead lever included in the linkage between the actuator and the brake shoes, a ratchet wheel secured to one of said elongated members, means carried by the dead brake lever for preventing rotation of the other of said elongated members, a pawl, means rotatably supporting said pawl for movement relative to said ratchet wheel, a mechanical connection between the live brake lever and the floating brake lever, ratchet-operating mechanism including a ratchet lever pivoted intermediate its ends to the actuator and movable with the actuator and the live brake lever, a stop rod having one end pivotally secured to one end of said ratchet lever, a support slidably supporting and engageable by said stop rod for limiting movement thereof in one direction only, and a mechanical connection extending between the other end of said ratchet lever and said pawl, movement of said ratchet lever with said linkage during a brake-applying operation rotating said pawl relative to said ratchet wheel, movement of said linkage beyond a predetermined amount being effective to move said pawl into a tooth-engaging position with said ratchet wheel, said ratchet-operating mechanism including a spring biasing said ratchet lever in a direction to maintain said stop rod against its support during automatic operation of the braking system and permitting movement of said stop rod away from said support during manual operation of the braking system to an abnormal braking position to increase the effective length of said stop rod, said ratchet-operating mechanism upon movement of the brake-applying linkage towards brake-releasing position rotating said pawl and said ratchet wheel to decrease the overall length of said telescopic members interconnecting the dead brake lever and the floating brake lever to decrease the extent of movement of the actuator necessary to move the brake shoes into their braking position.

21. In a braking system according to claim 16 the feature wherein said ratchet wheel secured to one of said elongated members is provided with a plurality of teeth and the distance between adjacent teeth corresponds to a predetermined displacement of the actuator.

22. In an automatic braking system having an actuator and associated brake-applying linkage for moving brake shoes into and out of braking positions, said actuator including a piston for power operation of the braking system to a normal braking position, and means manually operable for operating the braking system to an abnormal braking position, the improvement of brake-adjusting mechanism comprising adjustable members for varying the overall length of the linkage between the actuator and the brake shoes, a length-controlling element secured to one of said adjustable members, a second length-controlling element, means supporting said second element in cooperating relation with said first length-controlling element, operating mechanism for said length-controlling elements including a lever pivoted to the actuator, a support normally engaged by an element of said operating mechanism for preventing relative movement between said support and said element and producing movement of said pivoted lever in one direction only with movement of the linkage toward brake-applying position, yieldable means normally maintaining said element of said operating mechanism in engagement with said support during automatic operation of the braking system and permitting movement of said element away from said support during manual operation of the braking system to an abnormal braking position to increase the effective length thereof, and a mechanical connection between said lever and said lengthcontrolling elements, movement of the second one of said length-controlling elements with the linkage during a brake-applying operation beyond a predetermined amount conditioning the brake-applying linkage toward brakereleasing position to change the length of the linkage in a direction to reduce slack in the brake-applying linkage in movement of the brake shoes toward a braking position.

23. In a braking system according to claim 22 wherein said first length-controlling element comprises a member 21 having a plurality of teeth and the distance between adjacent teeth corresponds to a predetermined displacement of the actuator.

24. In a braking system according to claim 22 wherein said lever is substantially L-shaped and is pivotally carried by the actuator, one end of said lever being connected to said element, and said yieldable means comprises a spring carried by said element between the free end thereof and said support, said spring normally biasing said element against said support while permitting increase in the effective length of said element between said support and said lever upon movement of said element against the bias of said spring.

25. In a braking system according to claim 22 wherein said lever 'is pivoted intermediate its endsto a movable part of the linkage, said ends of said lever being angularly disposed with respect to each other, one end of said lever being connected to said element, and said yieldable means comprises a spring connecting said element and said support, said spring normally biasing said element against said support while permitting increase in the effective length of said element between said support and said lever upon movement of said element against the bias of said spring.

26. In a braking system, self-adjusting rod mechanism for reducing slack in the brake-applying linkage comprising rod means adjustable in length, a first length-controlling element carried by a member of said rod means, a second length-controlling element, rotatable means for supporting said second length-controlling element in cooperating relation with said first length-controlling element, means including a pivotal support for said second lengthcontrolling element for connecting said second lengthcontrolling element to a movable part of the brake-applying linkage, movement of said second length-controlling element by said connecting means beyond a predetermined amount during a brake-applying operation being efiective to move said second length-controlling element into a position of engagement with said first lengthcontrolling element for .movement of said member of said rod means during movement of the brake-applying linkage toward brake-releasing position to change the length of said rod means in a direction to reduce slack in the brake-applying linkage in movement of the brake shoes toward a braking position, and means on said pivotal support selectively operable on said second lengthcontrolling element solely upon rotation of said support ing means about the axis of said rod means a predetermined distance for reversing the efiect of said second length-controlling element on said first length-controlling element to reverse the direction of the change in length of said rod means thereby increasing the slack in the brake-applying linkage permitting replacement of the brake shoes.

27. In a braking system according to claim 26 wherein said first length-controlling element includes a plurality of teeth, said second length-controlling element comprises integral double finger pawl structure, said connecting means comprises a lever and a mechanical connection between said lever and said pawl structure, and means for maintaining one of said pawl fingers in cooperating relation with said teeth while the other of said pawl fingers is out of engagement with said teeth.

28. In a braking system, self-adjusting rod mechanism for reducing slack in the brake-applying linkage comprising rod means adjustable in length, a length-controlling element having a plurality of teeth and secured to and rotatable with a member of said rod means, a double finger pawl member supported in cooperating relation with the teeth of said length-controlling element, a lever pivoted to a movable part of the brake-applying linkage, a stop rod connected to one end of said lever, a support normally engaged by said stop rod for preventing relative movement between said support and said rod and producing movement of said pivoted lever in one direction only with movement of the lnkage toward brake-applying position, a mechanical connection between the other end of said lever and said double finger pawl mem-.

ber, rotation of said double finger pawl member by said lever beyond a predetermined amount during a brakeapplying operation being effective to move one of the fingers of said pawl into tooth-engaging position with a tooth of said length-controlling element-for rotation of said member of said rod means during movement of the brake-applying linkage toward brake-releasing position to change the length of the rod-means in a direction to reduce slack in the brake-applying linkage in movement of the brake shoes toward a braking position, said double finger pawl member including structure integral with both of said fingers, a pivot for said double finger pawl member, said pivot having a pair of cam surfaces in cooperative relation with said double finger pawl member to change the position of its fingers relative to said teeth,

and spring means operable on said structure for selectively biasing one or the other of said pawl fingers in cooperating relation with said teeth of said length-controlling element to reverse the direction of the change in length of said rod means.

29. In a braking system according to claim 28 wherein said stop rod comprises two sections pivotally connected, one of said sections normally engaging said lever pivoted to the movable part of the linkage to control the movement of said lever.

30. In a braking system, self-adjusting rod mechanism for reducing slack in the brake-applying linkage comprising rod means adjustable in length, a length-controlling element having a plurality of teeth and secured to and rotatable with a member of said rod means, a double finger pawl member supported in cooperating relation with the teeth of said length-controlling element, a lever pivoted to a movable part of the brake-applying linkage, a stop rod connected to one end of said lever, a support normally engaged by said stop rod for pre venting relative movement between said support and said rod and producing movement of said pivoted lever in one direction only with movement of the linkage toward brake-applying position, a mechanical connection between the other end of said lever and said pawl member, rotation of said pawl member by said lever beyond a predetermined amount during a brake-applying operation being effective to move said pawl into tooth-engaging position with a tooth of said-length-controlling element for rotation of said member of said rod means during movement of the brake-applying linkage toward brakereleasing position to change the length of the rod means in a direction to reduce slack in the brake-applying linkage in movement of the brake shoes toward a braking position, said double finger pawl member including structure integral with both of said fingers, and spring means operable on said structure for selectively biasing one or the other of the pawl fingers in cooperating relation with said teeth of said length-controlling element to reverse the direction of the change in length of said rod means, said stop rod comprising two sections pivotally connected, one of said sections normally engaging said lever pivoted to the movable part of the linkage to control the movement of said lever, said one of said sections including spaced stops, and said lever including a projection releasably connected with said one of said sections, said projection when released from its connection with said one of said sections being adapted for movement between said stops to limit the rotation of said lever about its pivot.

31. In a braking system, self-adjusting rod mechanism for reducing slack in the brake-applying linkage comprising rod means adjustable in length, a first length-controlling element including a plurality of teeth carried by a member of said rod means, a second length-controlling element comprising double finger pawl structure, a rotatable housing for supporting said pawl structure 

